A clustered file system includes two or more computers that share the same physical disks and that communicate with one another over a network so as to present a common view of a mounted file system to applications. Such applications may include incremental backup programs or other programs that are used to move a source file system from one set of physical disks to another set of physical disks while the source file system is still mounted and updated by running applications. Such backup programs seek to read a file non-disruptively. In particular, a backup program may utilize an on-disk snapshot of a file to perform a backup of the file, while at the same time, permitting other application tasks to utilize the file without having to wait for the backup to complete.